Document Type : Original Article
A significant number of pregnancies, especially
women with past histories of infertility, are associated
with fetal abnormalities (
The term translucency is used irrespective of whether
it is confined to the neck or envelopes the whole
fetus. In fetuses with chromosomal abnormalities,
cardiac defects and many genetic syndromes, the
NT thickness is increased (
In cases with increased NT and normal karyotype,
the frequency of fetal malformations, especially
heart defects, adverse pregnancy outcomes and
postnatal abnormalities is related to the NT thickness
Increased NT is also associated with congenital diaphragmatic
hernia (CDH) (
This study aimed to evaluate pregnant women at 11-14 weeks gestation and analyzed the proportion of high-risk and normal NT.
This was an analytic cross-sectional study performed
on 446 patients from the Fetal Medicine Unit in
Imam Khomeini Hospital, Ahvaz Jundishapur University
of Medical Sciences, Iran from 2009 to 2010.
NT scans were performed at 11-14 weeks gestations
with crown rump length (CRL) between 45-84 mm.
A certified sonographer performed all NT scans
using the Fetal Medicine Foundation (FMF) recommended
protocol. The ultrasound machine was
Me dison V20.First trimester affected fetuses have
a subcutaneous collection of fluid behind the neck
which can be easily envisioned by ultrasound as NT
Nuchal translucency test measurements. Figure A shows a normal fetus, figure B shows ultrasound picture of a 12-week gestation fetus with trisomy 21, demonstrating increased nuchal translucency thickness.
The study was approved by the University Hospital and Ahwaz Jundishapur University of Medical Sciences Ethics Committees, and all subjects granted informed consent to participate. For performing NT scans, the magnification of the image should be such that the fetal head and thorax occupy the whole screen as well as a middle sagittal view of the face should be obtained. The fetus should be in a neutral position, with the head aligned with the spine. When the fetal neck is hyper-extended, the measurement can be falsely increased and when the neck is flexed, the measurement can be falsely decreased. Care must be taken to distinguish between fetal skin and amnion.
The widest part of translucency must always be measured. Measurements should be taken with the inner border of the horizontal line of the calipers placed on the line that defines the nuchal translucency thickness. The crossbar of the caliper should be such that it is hardly visible as it merges with the white line of the border, not in the nuchal fluid.
FMF first trimester software was used for primary and secondary (adjusted) risk calculation. We used only NT for FMF software risk calculations due to unavailability of a Kryptor machine for measuring pregnancy associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (β-hCG) in our centre. We divided the results as low, intermediate and high-risk, and offered amniocentesis for high-risk women. Karyotype results of amniocentesis were checked.
All analysis was done using SPSS 16. Data were presented as numbers and percentages.
The mean maternal age was 28.5 ± 6 years. Eightyfive
percent of mothers were below 35 years old
and the remainder (15%) were 35 years of age and
Age distribution in total patients
The lowest CRL was 45 mm and the highest was 84 mm (average: 61.7 ± 9.82). Of these, 22% of CRL ranged between 45 to 54 mm, 42.2% between 55 to 64 mm, 25.3% between 65 to 74 mm and 10.5% between 75 to 84 mm. The mean gestational age was 12.4 ± 0.67 weeks (range: 11-13.6 weeks).
The average NT thickness was 1.75 mm. Distribution of NT and age with abnormal karyotype are shown in table 4. In reviewing the relationship between CRL and NT, a significant relationship was seen, which meansthe NT thickness increased by increasing the CRL length (p ≤ 0.001). There was no significant relationship between maternal age and NT (p=0.39).
There was a significant relationship between gestational
age and NT (p ≤ 0.001), that indicated with
increasing gestational age, NT increased. There
were 20 cases with increased adjusted risk (4.04%)
and 4 cases of documented abnormal karyotype
(0.9% and 28% of total and high-risk groups who
accepted amniocentesis, respectively). About 50%
of women with high-risk results were less than 35
years of age (
Age distribution in high-risk patients
|Age group||No (%)|
Of 6 cases with no amniocentesis, 3 had apparently normal fetuses at birth , one case was lost to follow up, one case ended in intra uterine fetal death (IUFD) at 26 weeks and in the last case pregnancy was terminated due to fetal major thalasemia diagnosed by chorionic vilus sampling in first trimester.
We observed 20 cases of increased adjusted risk and 4 cases of documented abnormal karyotype, which equaled 0.9% and 28% of total and highrisk groups that accepted amniocentesis, respectively.
According to a study by Monni et al. on the records of 32000 fetuses from 11 to 14 weeks gestation, a total of 16654 fetuses were studied by both NT measurement and nasal bone evaluation.
The median maternal age was 32 years (range: 14-49). In 854 fetuses (5.1%), NT was greater than
the 95th percentile and of these, 744 (87.1%) had
a normal karyotype. Among 141 (0.8%) diagnosed
cases of chromosomopathies, there were 96 cases
of trisomy 21. (
Zoppi et al. (
Among these, the NT thickness was increased in
28, and the nasal bone was absent in 13 (detection
rates of 90.3% and 41.9%, respectively) (
Outcome of amniocentesis and cytogenetic analysis in pregnant women
|Group||Total||Amniocentesis||Culture of amniotic fluid|
|Yes||No||Normal karyotype||Abnormal karyotype|
|normal at birth (n=3)||Down syndrome (n=1)|
|IUFD (n=1)||Turnersyndrome (n=1)|
|Major Thalassemia (n=1)||47XYY (n=1)|
|Notfollowed (n=1)||47XX-mar (n=1)|
In 5223 out of 5851 cases the fetal karyotype was
normal and in 628 cases it was abnormal (
Kagan et al. studied 11315 pregnancies. The median
maternal age was 34.5 (range: 15-50) years and
the median fetal crown-rump length was 64 (range
45-84) mm. The fetal karyotype was abnormal in
2168 (19.2%) pregnancies. The incidence of chromosomal
defects increased with NT thickness from
approximately 7% for those with NT between the
95th percentile for CRL and 3.4 mm, to 75% for
NT of 8.5 mm or more. In the majority of fetuses
with trisomy 21, the NT thickness was less than 4.5
mm, whereas in the majority of fetuses with trisomies
13 or 18 it was 4.5-8.4 mm, and in those with
Turner's syndrome it was 8.5 mm or more (
In our study increased adjusted risk was 4.04% and documented abnormal karyotype were 0.9% and 28% of total and high-risk groups who accepted amniocentesis, respectively. We showed that 50% of women with high-risk results and approximately half of abnormal karyotypes were noted in women under the age of 35 years. Therefore, if case screening tests are restricted to only women over the age of 35 years there is a chance that younger women with abnormal fetuses will be missed. In this study we showed that increased NT can identify not only trisomy 21, but also other numerous chromosomal anomalies such as Turner’s syndrome, 47 XYY and 47XX-mar. Knowing these risk factors may be important in pregnancy, particularly in patients with histories of infertility.